The invention relates to testing of semiconductor fabrication components.
High-precision manufacturing components are often tested for defects by manufacturers and consumers. Testing is most necessary where raw materials are expensive. Thus, for example, components used in semiconductor processing are frequently tested because the raw materials used in semiconductor manufacturing (new and partially processed wafers) are expensive.
Various techniques are available for testing the integrity of semiconductor processing components. One technique is x-ray radiography; in this technique the component is placed between an x-ray source and a sheet of photographic paper. The resulting image on the photographic paper can be used to detect voids in the manufactured component. A difficulty with this technique is that it does not detect other types of flaws in the component, e.g., cracks and other mechanical flaws in welds. Another difficulty with this technique is that it requires elaborate physical manipulation of the component and photographic paper to obtain a useful image, and therefore is difficult to implement as an automated operation on a production line.
A second testing technique is ultrasound testing; in this technique an ultrasonic transducer which generates ultrasonic energy is coupled to the component; ultrasonic energy reflected within the component is received by the transducer. A 2- or 3- dimensional CRT image of the internal structure of the component can be generated by moving the transducer into various locations across the surface of the component. The resulting image can be used to evaluate the strength of welds or other bonds in the component as well as locate voids or other imperfections.
Ultrasound testing (UT) requires acoustic coupling between the ultrasonic transducer and the object under test. In contact UT, the transducer is firmly pressed against the object under test as the transducer travels across the surface of the component. A difficulty with this technique is that a relatively sophisticated control procedure must be used to maintain tight contact between the component and the transducer as the transducer follows the surface of the component. This can make it difficult to implement contact UT as an automated operation on a component production line.
Immersion UT avoids this difficulty by immersing the component under test in a tank of liquid (typically, water). Ultrasonic energy can then be coupled into the component without making physical contact between the component and the ultrasonic transducer. Because immersion UT does not involve elaborate or precise physical manipulation of the component, it is relatively easier to implement as an automated operation on a component production line.
A difficulty with immersion UT is that the immersion liquid may react with and contaminate the surface of the immersed component, particularly where the component is manufactured of a "porous" material (e.g., Tungsten, Titanium, Iron, Terbium, Cobalt, Copper). Semiconductor manufacturing components such as sputtering targets are often made of such porous materials and therefore cannot be tested using immersion UT.